1. Field of the Invention
The present invention relates to a method of manufacturing an opto-electric hybrid board in which an optical waveguide and electrical wiring are combined, and to an opto-electric hybrid board obtained thereby.
2. Description of the Related Art
Recently, information and communications using light as a medium have come into widespread use. An opto-electric hybrid board in which an optical waveguide and electrical wiring are combined (see, for example, Japanese Patent Application Laid-Open No.2001-7463) has accordingly been employed as a board for use in electronic devices for information and communications and the like.
In general, this opto-electric hybrid board is structured such that an electrical wiring board including electrical interconnect lines (conductors) formed in a predetermined pattern and an optical waveguide including cores (optical interconnect lines) formed in a predetermined pattern and serving as a passageway for light are stacked together. An example of the opto-electric hybrid board is shown in FIG. 3. The opto-electric hybrid board B shown in FIG. 3 has a multi-layer structure having two layers in which an optical waveguide β is formed on an electrical wiring board α. In the above-mentioned electrical wiring board α, a plurality of electrical interconnect lines 96 are buried in an insulation layer 95 and are also supported by another insulation layer 94 in that state. In the above-mentioned optical waveguide β, a plurality of cores 93 are buried in an over cladding layer 98 and are also supported by an under cladding layer 92 in that state.
In the method of manufacturing the above-mentioned conventional opto-electric hybrid board B, however, the process of producing the optical waveguide β is performed after the process of producing the electrical wiring board α, and each of the processes involves the need for a multiplicity of steps. Thus, it takes a long period of time to manufacture the opto-electric hybrid board B. For example, the patterning of the electrical interconnect lines 96 in the electrical wiring board α involves the need for a large number of steps such as the steps of patterning a resist through exposure, development and the like, plating other portions than the resist, and then removing the above-mentioned resist. The patterning of the cores 93 in the optical waveguide β also involves the need for a large number of steps such as exposure, development and the like.
Additionally, the above-mentioned conventional opto-electric hybrid board B has the two-layer structure in which the optical waveguide β is stacked on top of the electrical wiring board α. Thus, the above-mentioned conventional opto-electric hybrid board B is disadvantageous in reducing the thickness thereof, and cannot respond to recent requests for the reduction in thickness.
In view of the foregoing, it is an object of the present invention to provide a method of manufacturing an opto-electric hybrid board which is capable of reducing the number of steps for the manufacture of the opto-electric hybrid board and which achieves the reduction in thickness of the opto-electric hybrid board to be manufactured, and an opto-electric hybrid board obtained thereby.
To accomplish the above-mentioned object, a first aspect of the present invention is intended for a method of manufacturing an opto-electric hybrid board, which comprising the steps of: forming a core-forming resin layer on an under cladding layer; forming a resist layer on the core-forming resin layer; forming the resist layer and the core-forming resin layer into a predetermined pattern by patterning to form the core-forming resin layer into cores; forming a thin metal film on the under cladding layer with the resist layer and the cores patterned so as to cover the resist layer and the cores; removing the resist layer covered with a portion of the thin metal film together with the portion of the thin metal film; electroplating the remaining portion of the thin metal film lying on side surfaces of the cores patterned to protrude and lying on a portion of the under cladding layer between the cores to fill grooves defined between adjacent ones of the cores with plated layers, thereby causing the plated layers to serve as electrical interconnect lines; and forming an over cladding layer so as to cover the cores and the electrical interconnect lines.
A second aspect of the present invention is intended for an opto-electric hybrid board obtained by the above-mentioned method of manufacturing the opto-electric hybrid board, which comprises: a plurality of protruding cores formed in a predetermined pattern on an under cladding layer; a thin metal film formed over side surfaces of the protruding cores and a surface portion of the under cladding layer except where the protruding cores are formed; electrical interconnect lines including electroplated layers buried in grooves defined between adjacent ones of the protruding cores; and an over cladding layer formed so as to cover the protruding cores and the electrical interconnect lines.
In the method of manufacturing the opto-electric hybrid board according to the present invention, the plurality of protruding cores (optical interconnect lines) are formed in a predetermined pattern, and thereafter the grooves defined between adjacent ones of the cores are filled with the plated layers obtained by the electroplating. The plated layers serve as the electrical interconnect lines (conductors). In other words, the electrical interconnect lines are produced by using the grooves defined between the cores serving as one of the components of an optical waveguide and the like. Thus, the present invention eliminates the need to form a new pattern of the electrical interconnect lines and accordingly reduces the number of steps for the manufacture of the opto-electric hybrid board. As a result, the present invention is capable of reducing the time required for the manufacture of the opto-electric hybrid board to achieve improvements in production efficiency. Further, since the pattern of the electrical interconnect lines is formed by using the pattern of the cores as mentioned above, the positioning accuracy of the cores and the electrical interconnect lines is automatically increased. Additionally, since the above-mentioned electrical interconnect lines are formed by using the grooves defined between the cores of the optical waveguide, the manufactured opto-electric hybrid board has what is called a single-layer structure, and is significantly thinner than the conventional opto-electric hybrid board having a two-layer structure.
When the under cladding layer is formed on the metal base, only the opto-electric hybrid board is easily obtained by removing only the above-mentioned metal base by etching after the opto-electric hybrid board is manufactured on the metal base.
In particular, when the metal base is a base made of stainless steel, the manufacture of the opto-electric hybrid board on the base is accomplished with stability because the base made of stainless steel is excellent in corrosion resistance and in dimensional stability.
The opto-electric hybrid board according to the present invention has what is called a single-layer structure because the electrical interconnect lines are formed by using the grooves defined between adjacent ones of the cores as mentioned above. Thus, the above-mentioned cores and the electrical interconnect lines are formed at the same vertical position. This enables the opto-electric hybrid board according to the present invention to be significantly thinner than the conventional opto-electric hybrid board having a two-layer structure.